after market radio wont turn off

i got a 03 gmc it has a aftermarket radio in it and last night was listing to music and went to turn it off and it wont turn off? I have replaced the box (wireing harness) because i was having problems with it and it fixed the problems but now it wont turn off and i didnt mess with anything just turned the key on and that wast it. If theres any ideas let me konw thanks!